The traditional way of using Aneros is to lightly contract the anus with your breathing, hold then let go.

However there's also the method to do nothing, presumably since the muscles will just contract it for you once they start to spasm and get excited. It means your mind isn't pent up having to focus on contracting and you can just think about the sensations.

But choices vary and lightly contracting + breathing is often the way to go, especially in learning how to feel for the prostate.

It is my understanding the Aneros motion is a little of both actions, in & out plus off & on. The design of the Aneros makes use of the three main pelvic floor muscle groups. Your anal sphincter muscles tend to make the Aneros slide in & out, your PC muscles tend to apply on/off pressure and your rectal muscles tend to push the Aneros into and against your prostate.

The unique patented design of the Aneros works by both sliding in & out and by pivoting about the abutment point (P-tab arm). The action of stimulating the perineum, anus and prostate simultaneously is why it works. The movement of the Aneros (via voluntary or involuntary contractions) is what makes the stimulation/massage effective. The extent of movement need not be much to be very effective, see the user Poll -> Aneros, How far does it move?

@sensitiveguy22, Your confusion is understandable given that there are multiple approaches to Aneros use. The Aneros WIKI mentions the two seemingly opposite approaches - contractions vs. 'do nothing'. Each man needs to experiment with a variety of techniques to find that which works best for him. Unfortunately, there is no ONE formula for success here, your unique personality, experiences, preferences, etc. all are factors influencing your practice. Try to be open minded in your approach, have fun and enjoy the learning process, after all you are here for the pleasure aren't you?

I practice both voluntary contractions at varying strengths and the "do nothing" technique and let the contractions naturally occur. Typically I will start out by totally relaxing my body for 15-30 minutes, then by that point I will already start to get involuntaries or I might toy with voluntary contractions. I find that if I start with voluntaries for a little after relaxed, then the involuntaries tend to come easier perhaps due to muscle fatigue leading to further relaxation. Either way I frequently make use of both techniques sometimes one more than the other to achieve equally pleasurable results.